Re: [Qemu-devel] [PATCH v2 3/3] virtio: Make disable-legacy/disable-modern compat properties optional

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Marc-André Lureau (marcandre.lureau@gmail.com) wrote:
> Hi
> 
> On Thu, Jan 10, 2019 at 6:05 AM Eduardo Habkost <ehabkost@redhat.com> wrote:
> >
> > The disable-legacy and disable-modern properties apply only to
> > some virtio-pci devices.  Make those properties optional.
> >
> > This fixes the crash introduced by commit f6e501a28ef9 ("virtio: Provide
> > version-specific variants of virtio PCI devices"):
> >
> >   $ qemu-system-x86_64 -machine pc-i440fx-2.6 \
> >     -device virtio-net-pci-non-transitional
> >   Unexpected error in object_property_find() at qom/object.c:1092:
> >   qemu-system-x86_64: -device virtio-net-pci-non-transitional: can't apply \
> >   global virtio-pci.disable-modern=on: Property '.disable-modern' not found
> >   Aborted (core dumped)
> >
> > Reported-by: Thomas Huth <thuth@redhat.com>
> > Fixes: f6e501a28ef9 ("virtio: Provide version-specific variants of virtio PCI devices")
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> > ---
> >  hw/core/machine.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index 5530b71981..a19143aa44 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -91,8 +91,9 @@ const size_t hw_compat_2_7_len = G_N_ELEMENTS(hw_compat_2_7);
> >
> >  GlobalProperty hw_compat_2_6[] = {
> >      { "virtio-mmio", "format_transport_address", "off" },
> > -    { "virtio-pci", "disable-modern", "on" },
> > -    { "virtio-pci", "disable-legacy", "off" },
> > +    /* Optional because not all virtio-pci devices support legacy mode */
> > +    { "virtio-pci", "disable-modern", "on",  .optional = true },
> > +    { "virtio-pci", "disable-legacy", "off", .optional = true },
> 
> Could the generic devices implement a specific interface instead?
> virtio-pci-generic?
> 
> Adding "optional" handling looks like it may hide some other errors.

I think it would be OK if it only ignored the non-existent property
errors (or better, tested for their existence and then skipped if
they weren't there).

Dave

> >  };
> >  const size_t hw_compat_2_6_len = G_N_ELEMENTS(hw_compat_2_6);
> >
> > --
> > 2.18.0.rc1.1.g3f1ff2140
> >
> >
> 
> 
> -- 
> Marc-André Lureau
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK